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Alkyl Groups

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Alkyl groups are not stable compounds themselves, they are simply parts of larger compounds. Alkyl groups are named by replacing the -ane ending of the parent alkane with an -yl ending.

Removing hydrogen atom from an alkane, and the remaining partial structure is called an alkyl group.
Straight chain alkyl groups are generated by removing a hydrogen from an end carbon, branched alkyl groups are generated by removing a hydrogen atom from an internal carbon.

For Example: removal of a hydrogen from ethane generates an ethyl group.

Definition

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In organic molecules alkyl groups typically consist of carbon atoms with a connectivity of four, with tetrahedral coordination geometry. This straightforward arrangement is not always mirrored in inorganic complexes, however, where alkyl groups have been reported to bind to metal atoms in a variety of modes.
For instance, methyl groups bridge between metal atoms in the dimer of trimethyl aluminium Me2Al($\mu$-Me)2AlMe2, thus giving five coordinate carbon atoms. And in tert-butyl lithium [(H3C)3CLi]4, the methyl groups bridge the triangular faces of a Li4 tetrahedron, and therefore contain six coordinate carbon atoms. These are classic examples from organometallic chemistry that serve to demonstrate that when placed close to a metal seemingly simple organic groups can present a variety of bonding interactions.

Naming

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Alkyl groups are named by replacing the -ane suffix of the alkane name with -yl, methane become methyl ethane becomes ethyl:

1) CH4 - methane, CH3 - methyl group
2) CH3-CH3 - ethane, CH3-CH2 - ethyl group
3) CH3-CH2-CH3 - propane, CH3-CH2-CH2 - propyl group
The following alkanes show the use of alkyl group nomenclature: 

Naming of Alkyl Groups

The names of most common alkyl groups, those having up to four carbon atoms. The propyl and butyl groups are simply unbranched three and four carbon alkyl groups. These groups are often named as "n-propyl" and "n-butyl" groups, to distinguish them from other kinds of branched propyl and butyl groups. 

List of Alkyl Groups
Each alkyl group is a collection of atoms that can be thought of as an alkane minus one hydrogen atom. The list of alkyl groups with the parent alkane and its structure is listed below.

Parent alkane Structure of parent alkane Structure of alkyl group Name of alkyl group
Methane CH4 CH3 methyl
Ethane CH3-CH3  CH3-CH2- ethyl
Propane  CH3-CH2-CH3  CH3-CH2-CH2-
CH3-CH(-)-CH3
propyl
Isopropyl
n-butane  CH3-CH2-CH2-CH3 CH3-CH2-CH2-CH2-
CH3-CH2-CH(-)-CH3
butyl
secondary butyl
iso butaneCH3-CH(CH2)-CH3CH3-CH(CH3)-CH2-
CH3-C(-)(CH3)-CH3
iso butyl
tertiary butyl